This invention relates to processes and systems for making food products from a feed stock that includes unrenneted casein and can include soluble proteins such as whey proteins. It also relates to food products obtained by such processes. In particular, this invention relates to cheese and cheese products which can incorporate soluble proteins, such as whey proteins.
A. Definitions of Terms
"Milk" means the lacteal secretion obtained by the milking of one or more females of a mammalian species, such as cow, sheep, goat, water buffalo, or camel. Broadly speaking, such milk is comprised of casein (a phospho-protein), soluble proteins, lactose, minerals, butterfat (milkfat), and water. The amount of these constituents in the milk may be adjusted by the addition of, or the removal of all or a portion of, any of these constituents. The term "milk" includes lacteal secretion whose content has been adjusted.
Milk obtained by milking one or more cows is referred to as "cows' milk". Cows' milk whose composition has not been adjusted is referred to herein as "whole milk". It is comprised of casein, whey proteins, lactose, minerals, butterfat (milkfat), and water. The composition of "cows' milk" can be adjusted by the removal of a portion of or all of any of the constituents of whole milk, or by adding thereto additional amounts of such constituents. The term "skim milk" is applied to cows' milk from which sufficient milkfat has been removed to reduce its milkfat content to less than 0.5 percent by weight. The term "lowfat milk" (or "part-skim milk") is applied to cows' milk from which sufficient milkfat has been removed to reduce its milkfat content to the range from about 0.5 to about 2.0 percent by weight.
The additional constituents are generally added to cows' milk in the form of cream, concentrated milk, dry whole milk, skim milk, or nonfat dry milk. "Cream" means the liquid, separated from cows' milk, having a high butterfat content, generally from about 18 to 36 percent by weight. "Concentrated milk" is the liquid obtained by partial removal of water from the whole milk. Generally, the milkfat (butterfat) content of concentrated milk is not less than 7.5 weight percent and the milk solids content is not less than 25.5 weight percent. "Dry whole milk" is whole milk having a reduced amount of water. It generally contains not more than five percent by weight of moisture on a milk solids not fat basis. "Nonfat dry milk" is the product obtained by the removal of water only from skim milk. Generally, its water content is not more than five weight percent and its milkfat content is not more than 1.5 weight percent.
Thus, the term "cows' milk" includes, among others, whole milk, low fat milk (part-skim milk), skim milk, reconstituted milk, recombined milk, and whole milk whose content has been adjusted.
The term "soluble proteins" means proteins that generally do not precipitate when a liquid (such as milk) containing such proteins is subjected to the conditions of a conventional cheese making process. Such proteins include, for example, whey proteins, soluble soybean proteins and egg white proteins.
The term "whey proteins" means cows' milk proteins that generally do not precipitate in conventional cheese making processes. The primary whey proteins are lactalbumins and lactoglobulins. Other whey proteins that are present in significantly smaller concentrations include euglobulin, pseudoglobulin, and immunoglobulins.
The term "feed stock" means a liquid which includes ingredients required to be present in cheese in required proportions, excluding water. However, the casein present in the feed stock is unrenneted casein, i.e. casein which has not been converted to paracasein. Such unrenneted casein includes native casein micelles, acid casein, sodium caseinate and calcium caseinate. The feed stock also may contain fat of dairy or nondairy origin, soluble proteins, carbohydrates, minerals and vitamins.
The term "high solids cheese" refers to cheeses which have a solids content higher than sixty percent by weight. These cheeses have been usually referred to in the trade as hard cheese. The term "very high solids cheese" refers to cheeses which have a solids content higher than seventy percent. Such cheeses have been referred to in the trade as very hard cheese.
In the conventional manufacture of cheese, milk is processed to produce a semi-solid mass called "cheese curd" (or "curd") and a liquid (whey). The curd contains casein, a small amount of lactose, most of the butterfat, minerals, and water. The whey contains whey proteins, most of the lactose, some of the butterfat, minerals, and water. The curd may be worked (e.g., stirred) and/or combined with certain flavor and taste producing ingredients, and/or ripened using bacteria to produce different varieties of "natural cheese".
One or more varieties of curd or natural cheese can be comminuted and mixed with an emulsifying agent to form, with the aid of heat, a homogeneous plastic mass called "processed cheese". Examples of processed cheese include: "process cheese", "process cheese food", "process cheese spread", and "process cheese product". The various types of processed cheeses are obtained depending on the processing conditions, the specific varieties of curds or natural cheeses used, and the additional ingredients added during the processing.
"Imitation cheese" is a food made in semblance of any natural cheese variety, processed cheese, or other foods made or natural or processed cheese, in which casein, caseinates, and/or safe or suitable non-milk ingredients, such as vegetable proteins, and vegetable oil, replace all or part of the nutritive milk components normally found in the food being simulated.
"Milk Clotting Enzymes" are those enzymes that are capable of coagulating milk. The term "renneting" refers to reaction on milk by a milk clotting enzyme.
"Unrenneted casein" refers to casein which has not been subjected to action of milk clotting enzymes.
B. The Problem this Invention Addresses
Natural cheese, such as Cheddar, stirred curd, Colby, Gouda, or Swiss, is made by coagulating milk that has been treated with suitable lactic acid producing bacteria to a suitable acidity, with appropriate milk clotting enzymes. The coagulum is cut and cooked resulting in curd and whey. The whey is drained from the curd, whereupon the curd may be Cheddared or stirred while additional acid is produced by fermentation of lactose to lactic acid in the curd. The curd may or may not be washed with water. If Cheddared, the curd is milled, whereupon it is salted and pressed into rectangular blocks or packed into barrels for maturing. The addition of lactic acid producing bacteria, ripening of the milk, cutting the curd, cooking the curd, stirring the curd, Cheddaring the curd and salting the curd are all controlled to yield a product in which the residual lactose and the unused buffer capacity of the curd are balanced so that complete fermentation of the residual lactose in the curd to lactic acid will result in a cheese having a pH suitable for market requirements, usually between 4.9 and 5.5.
The conventional processes for making natural and processed cheese utilize only casein. Whey proteins remain dissolved in the whey and are discharged as a by-product of the process. The whey proteins comprise about 14 to 24 weight percent of whole or skim milk's proteins and the nutritional value of the whey proteins is at least comparable to the nutritional value of casein. Accordingly, the loss of the whey proteins in the conventional cheese making processes limits the potential yields of such processes. The utilization of even a portion of the whey proteins in the manufacture of natural and processed cheeses is of great commercial importance.
Efforts have been made to design a process that would allow full utilization of the whey proteins in cheese making. One approach is to recover whey proteins from the whey by drying, condensing, ultrafiltration, or reverse osmosis of the whey. The recovered whey proteins are then combined with the cheese. Such processes are described, for example, in F. V. Kosikowski, Cheese and Fermented Foods, Edwards Brothers, Inc., Ann Arbor, Mich., 2 ed. 1977, pp. 451-458. A problem with this approach is that some countries have laws which prohibit, for most types of natural cheeses, recombining separately recovered whey proteins with the curd. For example, in the United States, whey proteins can be reincorporated into cheese curd only in making of certain natural cheeses, such as skim milk cheese. An additional problem associated with this approach is that the recovered whey constituents lack the physical and chemical characteristics required for making of natural cheese. For example, the dried whey proteins can be sprinkled into the cheese curd. However, only a limited amount of whey proteins can be added to cheese curd in this manner without changing its desired properties. Accordingly, the whey proteins recovered from whey are not used to any significant extent in commercial processes for making natural cheese. For these same reasons, whey proteins recovered in this manner are not used to any significant extent in the commercial manufacture of process cheeses. Moreover, it is commercially feasible to add only limited amounts of such recovered whey proteins to process cheese spreads, process cheese foods, process cheese products, or imitation cheeses.
Another approach for utilization of whey proteins in cheese making is to co-precipitate them with the casein. One process for obtaining coprecipitates of casein and whey proteins from milk is disclosed in U.S. Pat. No. 3,535,304 and in the corresponding Australian Patent No. 403,065 (hereinafter referred to as the Muller patents). The Muller patents specify that the product resulting from this process should find acceptance in some forms of baby food, ice cream, coffee whiteners, small goods, biscuits, bread, breakfast cereals, and canned processed foods. The final product of the Muller process lacks the "functionality" for making processed and imitation cheeses, i.e., it does not have the functional characteristics that are required for making such cheese. Another process for making cheese products from co-precipitates was developed by Schreiber Foods, Incorporated and described in U.S. patent application Ser. No. 202,237 filed on Oct. 30, 1980 now U.S. Patent No. 4,713,254. This process produces cheese products having the required functionality but it requires an adjustment of the pH of milk prior to coagulation which may cause problems with governmental regulations in some countries.
A further approach for increasing the yields of cheese making processes by utilization of the whey proteins is by ultrafiltration of milk. It has previously been proposed to produce products suitable for conversion into cheese by altering the composition of whole or skim milk utilizing ultrafiltration or reverse osmosis. The milk is contacted with a membrane which permits the passage of water, lactose, and some minerals, but prevents the passage of casein, the whey proteins, butterfat and some minerals. The selective concentration of milk results in the formation of a retentate which contains whey proteins. When retentate is coagulated by acid or rennet, it forms a coagulum which contains the whey proteins. If this coagulum is then subject to syneresis, some of the whey proteins are lost in the expressed whey. One method for producing cheese by ultrafiltration of milk is disclosed in U.S. Pat. No. 4,204,090 (Maubois, et al.) and in Australian Patent Specification No. 477,399. According to this method, whole or skim milk is concentrated by ultrafiltration to about one fifth of this volume to give a product, sometimes called a "liquid pre-cheese", which is then manufactured by conventional means to give cheese. This method, however, is only suitable for making soft cheeses of the Camembert or Reblochon type and possibly, some semi-hard cheeses. It cannot
used to produce harder cheese of the Cheddar, Colby, or stirred-curd type, because the water content of the pre-cheese is too high and the ratio of buffer capacity to lactose will not give the desired final pH in the product.
In 1980 C. A. Ernstrom, B. J. Sutherland and G. W. Jameson published an article entitled "Cheese Base for Processing: A High Yield Product from Whole Milk by Ultrafiltration" in Journal of Dairy Science, Vol. 63, 228-234. In the process described in this article, the moisture content and pH of the final product is controlled to any desired level. The process results in a cheese base which has a moisture content and pH appropriate for use in place of conventionally made natural cheeses in the production of process cheeses. In the Ernstrom, et al. process, whole milk of normal pH or acidified to pH 5.7 is concentrated by ultrafiltration to 40% original milk weight and diafiltered at constant volume until a desired ratio of lactose to buffer capacity is established. The retentate is further concentrated by ultrafiltration to 20% of the original milk weight. The retentates are then inoculated with cheese starter and incubated to completely ferment the residual lactose. Precise control of final pH is achieved by controlling the level of lactose through diafiltration.
The fermented retentate is converted in a batch manner to cheese base in a swept-surface vacuum pan evaporator. The cheese base can be used to replace the unripened natural cheese component of processed cheese as it has the same pH and gross composition of Cheddar cheese. The use of the batch evaporator is necessitated by the fact that the retentate upon fermentation forms a curd or coagulum. Such a product cannot be readily processed in any continuous flow evaporator. Accordingly, the overall process of Ernstrom, et al. is essentially a batch process.
Subsequently, Jameson and Sutherland devised a continuous process for making cheese containing casein and whey proteins. This process has been commercialized by Schreiber Foods, Inc. It is described in European Patent Specification No. 0 065 981 published on Aug. 12, 1982. In the Jameson et al. process the ionic strength of the milk is increased so as to maintain the milk in the liquid state and to prevent the formation of any coagulum. The process includes the steps of selectively concentrating milk, fermenting the milk to produce a product having the solids composition as desired in cheese or cheese base and containing substantially all of the casein and whey proteins which were originally present in the milk and removing water from the product to achieve the desired moisture content. However, this process has not been commercially used to make high or very high solids cheese with varying texture as desired.
Another process developed by PASILAC for making cheese that incorporates whey protein by ultrafiltration is described in U.S. Pat. No. 4,401,679. This process includes the ultrafiltration and diafiltration of milk followed by inoculating the retentate with culture prior to evaporation and the subsequent fermentation of the cheese to a lower pH finished product. Since the evaporation of the retentate takes place at relativley high pH and the casein is not converted to paracasein by milk clotting enzyme (such as rennet) treatment, this process does not produce high solids hard cheese with the typical flavor, body and texture.
European Patent Application 0 174 847 published Mar. 19, 1986 describes another approach to making cheese which includes whey proteins. Briefly, the milk is converted by ultra and diafiltration into a retentate. The retentate is fermented without coagulation and contacted with a non-coagulating amount of milk clotting enzyme. The retentate is then evaporated to produce pre-cheese which is held at curing conditions to convert more than 65 percent of Kappa casein to para Kappa casein. The cured pre-cheese is texturized by mechanical working of the pre-cheese to produce cheese having acceptable texture. This texturization step can not take place until at least about 65% of the available Kappa casein is converted to para Kappa casein. This conversion is effected in about 3 days to 14 days after pre-cheese is removed out of evaporator. Therefore, the process is inefficient. The process is said to be capable of producing cheese having over 60% solids by weight.
The European Patent Application No. 0 174 846 published Mar. 14, 1986 describes a similar process except that the fermented retentate is maintained in a quiescent state during evaporation. The process is said to be capable of producing a cheese curd having solids content of more than about 50 percent by weight. This process is inefficient for the same reason in that it requires conversion of at least 65% of Kappa casein to para Kappa casein which requires from 3 to 14 days. Additionally, to achieve the well knitted texture, the cheese curd has to be pressed overnight and maintained in a 45.degree. F. cooler for about 10 days.
Thus, the prior attempts have been unsuccessful in devising an efficient, economical, readily controllable, continuous process that can produce cheese that has varied textures and solid levels up to above 70% by weight and that can include high levels of soluble proteins. There is, therefore, an unsatisfied, long-felt need for such a process, products made by such process and system for making such products.